U.S. patent number 5,352,564 [Application Number 08/184,171] was granted by the patent office on 1994-10-04 for resist compositions.
This patent grant is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Toshinobu Ishihara, Ken'ichi Itoh, Kazumasa Maruyama, Yoshihumi Takeda.
United States Patent |
5,352,564 |
Takeda , et al. |
October 4, 1994 |
Resist compositions
Abstract
A resist composition comprising a base resin, an acid release
agent, and a dissolution inhibitor is improved in sensitivity and
resolution when the base resin is typically selected from
poly-t-butoxystyrene/poly-hydroxystyrene,
poly-t-butoxystyrene/poly-p-methoxymethoxystyrene/polyhydroxystyrene,
and poly-t-butoxystyrene/poly-p-methoxystyrene/polyhydroxystyrene
copolymers. The composition forms a resist useful for the
manufacture of LSI.
Inventors: |
Takeda; Yoshihumi (Niigata,
JP), Ishihara; Toshinobu (Niigata, JP),
Itoh; Ken'ichi (Niigata, JP), Maruyama; Kazumasa
(Niigata, JP) |
Assignee: |
Shin-Etsu Chemical Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
27520571 |
Appl.
No.: |
08/184,171 |
Filed: |
January 19, 1994 |
Foreign Application Priority Data
|
|
|
|
|
Jan 19, 1993 [JP] |
|
|
5-023770 |
Jan 19, 1993 [JP] |
|
|
5-023771 |
Apr 19, 1993 [JP] |
|
|
5-115306 |
Apr 19, 1993 [JP] |
|
|
5-115307 |
Apr 19, 1993 [JP] |
|
|
5-115308 |
|
Current U.S.
Class: |
430/270.1;
522/150; 522/160; 430/326; 430/909 |
Current CPC
Class: |
G03F
7/039 (20130101); G03F 7/0758 (20130101); Y10S
430/11 (20130101) |
Current International
Class: |
G03F
7/075 (20060101); G03F 7/039 (20060101); G03C
001/492 () |
Field of
Search: |
;430/270,325,326
;522/150,160 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brammer; Jack P.
Attorney, Agent or Firm: Millen, White, Zelano, &
Branigan
Claims
We claim:
1. A resist composition comprising a base resin, an acid release
agent capable of generating an acid upon exposure to light, and a
dissolution inhibitor containing an acid unstable group, said base
resin being represented by the following rational formula (1), (2)
or (3): ##STR29## wherein each of R.sup.1 and R.sup.3 is a hydrogen
atom or methyl group, R.sup.2 is a tert-butyl group, and letters a
and b satisfy a+b=1, ##STR30## wherein each of R.sup.1, R.sup.3 and
R.sup.5 is a hydrogen atom or methyl group, R.sup.4 is a tert-butyl
group, R.sup.6 is an acid hydrolyzable group selected from the
group consisting of methoxymethyl, tetrahydro-pyranyl,
trialkylsilyl, isopropoxymethyl, tetrahydrofuranyl, and
tert-butoxycarbonyl groups, and letters c, d and e satisfy c+d+e=1,
##STR31## wherein each of R.sup.1, R.sup.3 and R.sup.5 is a
hydrogen atom or methyl group, R.sup.7 is selected from the group
consisting of tert-butyl, methoxymethyl, tetrahydropyranyl, and
trialkylsilyl groups, and R.sup.8 is a lower alkoxy group or a
hydrogen atom, and letters f, g and h satisfy f+g+h=1.
2. A resist composition according to claim 1 wherein said base
resin has a molecular weight dispersity Mw/Mn of 1.0 to 1.4.
3. A resist composition as in claim 1, wherein the base resin is of
the rational formula (1) ##STR32##
4. A resist composition according to claim 3, wherein said base
resin has a molecular weight dispersity Mw/Mn of 1.0 to 1.4.
5. A resist composition as in claim 1, wherein the base resin is of
the rational formula (2) ##STR33##
6. A resist composition according to claim 5, wherein said base
resin has a molecular weight dispersity Mw/Mn of 1.0 to 1.4.
7. A resist composition as in claim 1, wherein the base resin is of
the rational formula (3) ##STR34##
8. A resist composition according to claim 7, wherein said base
resin has a molecular weight dispersity Mw/Mn of 1.0 to 1.4.
9. A resist composition as in claim 1, wherein the base resin is of
the rational formula ##STR35## wherein a+b=1 ##STR36## wherein
c+d+e=1 or ##STR37## wherein f+g+h=1.
10. A resist composition as in claim 9, wherein the acid release
agent is ##STR38##
11. A resist composition as in claim 9, wherein the dissolution
inhibitor is 2,2,bis[p-(t-butoxycarboxyloxy)-phenylpropane.
12. A resist composition as in claim 1, wherein the base resin is a
poly-tert-butoxy-.alpha.-methylstyrene, polyhydroxystyrene or of
the rational formulae ##STR39## wherein a+b=1; a+d+e=1, and
f+g+h=1.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a resist composition of the chemical
amplification type for use in forming fine patterns upon
manufacture of super LSIs.
2. Prior Art
With the advance of LSI technology, the memory capacity of IC chips
reaches an order of mega bits and a rule of submicron is thus
required for the fineness of wiring pattern. Accordingly,
lithography light sources are shifting toward shorter wavelength
from the ultraviolet band to the deep ultraviolet band which is
more advantageous for fine patterning. Also, the current mainstream
of etching step involved in the LSI manufacturing process is dry
etching using RF plasma.
In these circumstances, the lithography technology uses resists
which have to be sensitive and transmissive to the wavelength used
and resistant against dry etching. More particularly, novolak type
resins and other aromatic resins are useful resists for use in
photolithography, especially g and i-ray lithography in view of
light transmittance at the wavelength used and plasma etching
resistance.
However, the light source intensity of deep ultraviolet light
including mercury line spectrum on a shorter wavelength side than g
and i-rays and excimer laser light such as KrF and ArF is extremely
weaker than the light source intensity of g and i-rays. Utilization
of such deep-UV light in photolithography has the problem that
prior art resists conventionally used with g and i-rays provide
unacceptable exposure sensitivity and low light transmittance to
deep-UV light. There is a need for a new type of resist.
Resists of the chemical amplification type were developed as a
substitute for the conventional resists. For example, Japanese
Patent Application Kokai (JP-A) No. 45439/1984 discloses a resist
composition comprising
p-tert-butoxycarbonyloxy-.alpha.-methylstyrene which is one of
polymers having acid unstable, recurring branched groups and a
diaryl iodonium salt which is one of photo-polymerization
initiators capable of generating acid upon exposure to radiation.
Upon exposure of the resist to deep-UV light, the diaryl iodonium
salt decomposes to generate an acid which in turn, causes cleavage
of the p-tert-butoxy-carbonyl group of
p-tert-butoxycarbonyloxy-.alpha.-methylstyrene into a polar group.
Then a desired pattern is obtained by dissolving away the thus
exposed areas or unexposed areas with base or non-polar
solvent.
JP-A 115440/1987 discloses a resist composition comprising
poly-4-tert-butoxy-.alpha.-methylstyrene and di(tert-butylphenyl)
iodonium trifluoromethane sulfonate which are dissolved in diglyme
and then exposed to deep-UV light. This resist achieves a high
degree of resolution through the same reaction mechanism as the
resist of JP-A 45439/1984.
Like the resist composition comprising poly-4-tert-butoxystyrene
and an acid release agent disclosed in JP-A 115440/1987, JP-A
223858/1991 discloses a two-component system resist composition
comprising a resin having a tert-butoxy group in its molecule and
an acid release agent and JP-A 211258/1992 discloses a
two-component system resist composition comprising a
polyhydroxystyrene containing a methyl, isopropyl, tert butyl,
tetrahydro-pyranyl or trimethylsilyl group in its molecule and an
acid release agent.
The polymers used in these well-known resists as a major component
are obtained by conventional radical or cationic polymerization of
corresponding monomers. Since no special attention was paid to the
molecular weight distribution of polymers, there were obtained
polymers having a broad and uneven molecular weight distribution.
Another base polymer of the chemical amplification type used in
conventional resist compositions is a hydroxy-styrene resin in
which some hydroxyl groups are replaced by tert-butoxycarbonyloxy
groups (abbreviated as t-Boc groups). This resin is thermally
unstable and the t-Boc groups are readily split off.
In these two-component system positive resist compositions
comprising a hydroxystyrene resin in which hydroxyl groups are
protected with protective groups and an acid release agent, many
protective groups must be decomposed in exposed areas before the
resist film can be dissolved in a developer. This undesirably
leaves the increased possibility of changing film thickness and
introducing stresses and bubbles in the film.
A number of chemical amplification type positive resist
compositions have been proposed as mentioned above although they
have some problems and are difficult to use in practice.
SUMMARY OF THE INVENTION
Making investigations on a chemical amplification type resist
composition having high sensitivity, high resolution, process
adaptability, and commercial applicability, the inventors have
found that when an acid release agent, typically an onium salt and
a dissolution inhibitor containing an acid unstable group are
blended with a resin of the rational formula (1), (2) or (3) shown
below as a base resin, there is obtained a resist composition which
minimizes the possibility of changing film thickness and generating
bubbles because the amount of dissolution inhibitor which is to be
decomposed with the acid is reduced and which is advantageous in
precise fine patterning and useful as a resist material for the
manufacture of super LSIs. ##STR1##
Each of R.sup.1 and R.sup.3 is a hydrogen atom or methyl group and
R.sup.2 is a tert-butyl group. Letters a and b satisfy a+b=1.
##STR2##
Each of R.sup.1, R.sup.3 and R.sup.5 is a hydrogen atom or methyl
group, R.sup.4 is a tert-butyl group, and R.sup.6 is an acid
hydrolyzable group selected from the group consisting of
methoxymethyl, tetrahydro-pyranyl, trialkylsilyl, isopropoxymethyl,
tetrahydrofuranyl, and tert-butoxycarbonyl, groups. Letters c, d
and e satisfy c+d+e=1. ##STR3##
Each of R.sup.1, R.sup.3 and R.sup.5 is a hydrogen atom or methyl
group, R.sup.7 is selected from the group consisting of tert-butyl,
methoxymethyl, tetrahydropyranyl, and trialkylsilyl groups, and
R.sup.8 is a lower alkoxy group such as a methoxy and ethoxy group
or a hydrogen atom. Letters f, g and h satisfy f+g+h=1.
When the base resin of formula (1), (2) or (3) is a narrow disperse
polymer having a molecular weight dispersity Mw/Mn of 1.0 to 1.4,
the resolution is substantially increased in that good resolution
is achieved to a level of 0.4 .mu.m or less upon exposure to
excimer laser light.
Note that the dispersity used herein is a molecular weight
distribution defined as the weight average molecular weight divided
by the number average molecular weight, i.e., Mw/Mn.
The base resin of formula (1) is known as a major component of
resist materials. The polymers used in well-known resists as a
major component are obtained by conventional radical or cationic
polymerization of corresponding monomers. Since no special
attention was paid to the molecular weight distribution of polymers
or no means was taken for controlling the distribution, there were
obtained polymers having a broad and uneven molecular weight
distribution. We have found that these polymers having a broad
dispersity do not well accommodate excimer laser light. In order to
enhance resolution enough to provide a ultra-fine pattern by
exposure to excimer laser light, the base resin of formula (1)
should advantageously have a dispersity Mw/Mn of 1.0 to 1.4,
preferably 1.0 to 1.3.
By using a polymer having such a narrow dispersity, there is
obtained a heat resistant resin. By using a resin of such design as
a major component, there is obtained a resist composition which has
sufficient sensitivity upon exposure to UV and deep-UV light and
which eliminates a lowering of light intensity, a lowering of
vacuum during a vacuum step in the wafer manufacturing process,
contamination of the processing atmosphere, and retardation of
polymer dissolving rate, and thus eliminates unstable factors
involved in patterning. The composition is thus useful as a resist
material for the manufacture of super LSIs.
According to the present invention, there is provided a chemical
amplification type resist composition comprising (A) a base resin
represented by the rational formulae (1), (2) or (3), (B) an acid
release agent capable of generating an acid upon exposure to light,
and (C) a dissolution inhibitor containing an acid unstable
group.
DETAILED DESCRIPTION OF THE INVENTION
In a first form of the chemical amplification type resist
composition of the present invention, the base resin used in the
composition as the major component (A) is a polymer of the
following rational formula (1): ##STR4## wherein each of R.sup.1
and R.sup.3 is a hydrogen atom or methyl group, R.sup.2 is a
tert-butyl group, and letters a and b satisfy a +b =1.
In order to achieve high resolution, the polymer of formula (1)
should preferably have a dispersity Mw/Mn of 1.0 to 1.4, more
preferably 1.0 to 1.3. A dispersity of more than 1.4 tends to incur
a substantial lowering of resolution.
In formula (1) wherein a+b=1, it is recommended from the
standpoints of film retention, resolution and pattern configuration
that a is in the range of 0.05 to 0.5, preferably 0.1 to 0.3, more
preferably 0.12 to 0.25.
The polymer can be prepared, for example, by polymerizing
p-tert-butoxystyrene or p-tert-butoxy-.alpha.-methylstyrene monomer
into poly-p-tert-butoxystyrene or
poly-p-tert-butoxy-.alpha.-methylstyrene and splitting off some of
ether bonds in the polymer. This polymerization may be effected by
any desired method including radical, cationic and anionic
polymerization methods.
The resulting polymer is optionally worked up and isolated by
adding methanol to the reaction mixture to cause precipitation,
followed by washing and drying. In general, a polymer as reacted
contains impurities such as unreacted reactants and by-products and
if a composition containing this polymer is used as a resist in the
manufacture of super LSI, the impurities can adversely affect the
wafer manufacturing process. Therefore, full purification of the
polymer is recommended. Additionally, since resist properties
largely depend on the molecular weight dispersity of the polymer,
it is preferred to control the molecular weight distribution by any
desired method, for example, by removing a low molecular weight
moiety by fractionation, so that the dispersity may fall in the
range of 1.0 to 1.4.
Next, ether bonds in the polymer are partially split off with an
acid, obtaining a polymer represented by rational formula (1). This
scission reaction of ether bonds is readily carried out by
dissolving the polymer in a solvent such as dioxane, acetone,
acetonitrile and benzene or a mixture thereof, and adding dropwise
an acid such as hydrochloric acid, hydrobromic acid,
para-toluenesulfonate pyridinium salt and trifluoroacetic acid. The
degree of splitting off varies with the amount of acid added. In
the case of hydrochloric acid, for example, the degree of splitting
off is controlled by suitably selecting the amount of hydrochloric
acid in the range of 0.1 to 2 times the moles of ether bonds.
Preferably the value of a representative of the residual proportion
of ether bonds is controlled to fall in the range of 0.05 to 0.5,
more preferably 0.1 to 0.3, most preferably 0.12 to 0.25.
In a second form of the resist composition of the present
invention, the base resin used as the major component (A) is a
polymer of the following rational formula (2): ##STR5## wherein
each of R.sup.1, R.sup.3 and R.sup.5 is a hydrogen atom or methyl
group, R.sup.4 is a tert-butyl group, R.sup.6 is an acid
hydrolyzable group selected from the group consisting of
methoxymethyl, tetrahydro-pyranyl, trialkylsilyl, isopropoxymethyl,
tetrahydrofuranyl, and tert-butoxycarbonyl groups, and letters c, d
and e satisfy c+d+e=1.
The polymer of formula (2) can be prepared, for example, by
effecting block or random copolymerization between a
p-tert-butoxystyrene or p-tert-butoxy-.alpha.-methylstyrene and one
or more monomers of p -methoxymethoxystyrene,
p-tetrahydropyranyloxystyrene and p-trimethylsiloxystyrene to form
a copolymer of the rational formula (4) shown below, and treating
the copolymer with an acid to partially and selectively split off
only tert-butoxy groups. ##STR6## It is understood that c'+d=1 in
formula (4) and c +d+e=1 in formula (2).
The polymerization to form a copolymer of formula (4) may be
effected by any desired method including radical, cationic and
anionic polymerization methods.
The resulting copolymer of formula (4) is optionally worked up and
isolated by adding methanol to the reaction mixture to cause
precipitation, followed by washing and drying. As previously
mentioned, if a composition based on a polymer containing
impurities is used as a resist in the manufacture of super LSI, the
impurities can adversely affect the wafer manufacturing process.
Therefore, full purification of the polymer is recommended.
Additionally, since resist properties largely depend on the
molecular weight dispersity of the polymer, it is preferred to
control the molecular weight distribution by any desired method,
for example, by removing a low molecular weight moiety from the
copolymer of formula (4) by fractionation, so that the dispersity
may fall in the range of 1.0 to 1.4, preferably 1.0 to 1.3.
Next, only ether bonds of R.sup.4 in the copolymer of formula (4)
are partially and selectively split off with an acid, obtaining a
copolymer represented by rational formula (2). Scission of
tert-butoxy groups is readily carried out by dissolving the polymer
in a solvent such as dioxane, acetone, acetonitrile and benzene or
a mixture thereof, and adding dropwise an acid such as hydrochloric
acid, hydrobromic acid, para-toluenesulfonate pyridinium salt and
trifluoroacetic acid. The degree of splitting off varies with the
amount of acid added. In the case of hydrochloric acid, for
example, the degree of splitting off is controlled by suitably
selecting the amount of hydrochloric acid in the range of 0.1 to 2
times the moles of ether bonds. It is recommended from the
standpoints of film retention, resolution and pattern configuration
that the value of c representative of the residual proportion of
tert-butoxy groups (R.sup.4) is controlled to fall in the range of
0.05 to 0.45, more preferably 0.1 to 0.25. It is also preferred
that d is in the range of 0.05 to 0.25, especially 0.05 to 0.2 and
e is in the range of 0.5 to 0.9, especially 0.7 to 0.85.
In a third form of the resist composition of the present invention,
the base resin used as the major component (A) is a polymer of the
following rational formula (3): ##STR7## wherein each of R.sup.1,
R.sup.3 and R.sup.5 is a hydrogen atom or methyl group, R.sup.7 is
a tert-butyl, methoxymethyl, tetrahydropyranyl, or trialkylsilyl
group, R.sup.8 is a lower alkoxy group such as a methoxy and ethoxy
group or a hydrogen atom, and letters f, g and h satisfy
f+g+h=1.
The polymer of formula (3) can be prepared, for example, by
copolymerizing a mixture of a first monomer such as
p-methoxystyrene, p-methoxy-.alpha.-methylstyrene, p-ethoxystyrene,
and p-ethoxy-.alpha.-methylstyrene and a second monomer such as
p-tert-butoxystyrene, p-tetrahydropyranyloxystyrene,
p-trimethylsiloxystyrene, and p-methoxymethoxystyrene to form a
copolymer of the rational formula (5) shown below, and treating the
copolymer with an acid to partially and selectively split of only
tert-butoxy groups. ##STR8## It is understood that f'+g=1 in
formula (5) and f+g+h=1 in formula (3).
The polymerization to form a copolymer of formula (5) may be
effected by any desired method including radical, cationic and
anionic polymerization methods.
The resulting copolymer of formula (5) is optionally worked up and
isolated by adding methanol to the reaction mixture to cause
precipitation, followed by washing and drying. As previously
mentioned, if a composition base on a polymer containing impurities
is used as a resist in the manufacture of super LSI, the impurities
can adversely affect the wafer manufacturing process. Therefore,
full purification of the polymer is recommended. Additionally,
since resist properties largely depend on the molecular weight
dispersity of the polymer, it is preferred to control the molecular
weight distribution by any desired method, for example, by removing
a low molecular weight moiety from the copolymer of formula (5) by
fractionation, so that the dispersity may fall in the range of 1.0
to 1.4, preferably 1.0 to 1.3.
Next, only ether bonds of R.sup.7 in the copolymer of formula (5)
are partially and selectively split off with an acid, obtaining a
copolymer represented by rational formula (3). Scission of
typically tert-butoxy groups is readily carried out by dissolving
the polymer in a solvent such as dioxane, acetone, acetonitrile and
benzene or a mixture thereof, and adding dropwise an acid such as
hydrochloric acid, hydrobromic acid, para-toluenesulfonate
pyridinium salt and trifluoroacetic acid. The degree of splitting
off varies with the amount of acid added. In the case of
hydrochloric acid, for example, the degree of splitting off is
controlled by suitably selecting the amount of hydrochloric acid in
the range of 0.1 to 2 times the moles of ether bonds. It is
recommended from the standpoints of film retention, resolution and
pattern configuration that the value of f representative of the
residual proportion of tert-butoxy groups (or other groups
represented by R.sup.7) is controlled to fall in the range of 0.04
to 0.3, more preferably 0.1 to 0.2. It is also preferred that q is
in the range of 0.01 to 0.3, especially 0.01 to 0.1 and h is in the
range of 0.4 to 0.95, especially 0.7 to 0.89.
Component (B) in the resist composition of the invention is an acid
release agent capable of generating an acid upon exposure to light,
which is typically an onium salt cationic photo-initiator. The acid
release agent is to generate strong acid upon exposure to light. In
a wafer stepper, the onium salt in the exposed resist film is
decomposed to generate strong acid which in turn, causes cleavage
of OR groups in the polymer of formula (1) to (3) into hydroxyl
groups as shown below whereby the polymer becomes alkali soluble.
It is understood that R is R.sup.2, R.sup.4, R.sup.6 or R.sup.7.
##STR9##
Typical of the acid release agent are onium salt cationic
photo-initiators, examples of which are given below. ##STR10##
Other useful onium salt cationic photo-initiators are disclosed in
JP-A 45439/1984, 440/1987, and 300250/1989, and U.S. Pat. No.
4,537,854. The onium salts are not limited to these examples and
any substances capable of generating acid upon exposure to light
may be used.
Preferably the acid release agents or onium salt cationic
photo-initiators are blended in amounts of about 0.1 to about 15%
by weight, more preferably about 0.5 to about 5% by weight of the
resist composition. With less than 0.1% by weight of the acid
release agent, the composition would have low sensitivity though it
still retains positive resist performance. As the amount of acid
release agent increases, the resist is increased in sensitivity.
Above 15% by weight of the acid release agent, no further increase
of sensitivity is expected though the composition still retains
positive resist performance. Since the acid release agent is an
expensive reagent and an increase of a low molecular weight
component in the resist can lower the mechanical strength of a
resist film, it is recommended to add the acid release agent in an
amount of up to 15% by weight.
In the resist composition of the invention, component (C) or
dissolution inhibitor having an acid unstable group such as
tert-butoxy, tert-butoxycarbonyloxy, tert-butoxycarbonylmethyl and
the like is blended with the above-mentioned components (A) and
(B). Exemplary dissolution inhibitors are derivatives of
bisphenol-A in which at least one OH group is replaced by a
tert-butoxy or tert-butoxycarbonyloxy (t-Boc) group. Other
exemplary dissolution inhibitors are shown below. It is preferred
from the standpoint of resolution that at least one acid unstable
group is a tert-butoxycarbonyloxy group. ##STR11##
The dissolution inhibitor is preferably blended in an amount of 5
to 40% by weight of the entire resist composition. Less than 5% by
weight of the dissolution inhibitor would provide less dissolution
inhibition effect whereas more than 40% by weight of the
dissolution inhibitor would adversely affect mechanical strength,
heat resistance and resolution.
The resist composition of the present invention is generally
prepared by dissolving components (A), (B) and (C) in a multiple
amount of an organic solvent. The organic solvent used herein is
desirably one in which the respective components are fully soluble
and which allows for uniform spread of a resist film. Examples
include butyl acetate, xylene, acetone, cellosolve acetate,
ethylene glycol monomethyl ether, diethylene glycol monomethyl
ether, ethylene glycol monoethyl ether, diethylene glycol dibutyl
ether, diethylene glycol dimethyl ether (diglyme), ethyl lactate,
methyl lactate, propyl lactate, and butyl lactate alone or in
admixture of two or more.
The use and light exposure of the resist composition may be in
accord with the well-known conventional lithography. In particular,
the resist composition of the invention is adapted for fine
patterning with deep-ultraviolet light having a wavelength of 254
to 193 nm.
There has been described a positive resist composition which is
sensitive to high energy radiation and improved in sensitivity,
resolution and plasma etching resistance, and yields a resist
pattern having higher heat resistance. The resist pattern has
little tendency of overhanging, implying improved dimensional
control. By virtue of these advantages, especially reduced
absorption at the exposure wavelength of a KrF excimer laser, a
fine pattern having perpendicular walls to the substrate can be
readily formed.
EXAMPLE
Examples of the present invention are given below by way of
illustration and not by way of limitation. Mw is a weight average
molecular weight and the dispersity is a molecular weight
distribution Mw/Mn.
Synthesis 1
A 500-ml flask was charged with 2.4 grams of
2,2'-azobisisobutylnitrile, 60 grams of p-tert-butoxystyrene, and
120 ml of benzene and purged with nitrogen. The mixture was subject
to polymerization at 90.degree. C. for 7 hours. The resulting
polymer was washed with methanol and dried. On analysis by gas
permeation chromatography (GPC), the polymer had a Mw of 17,000 and
a dispersity of 2.01. The yield was 70%.
The polymer was further dissolved in a benzene/methanol solvent
mixture for fractionation. The polymer was dried again, obtaining
29 grams of poly-p-butoxystyrene having a Mw of 15,000 and a
dispersity of 1.35. This is designated Polymer A.
By a similar procedure, p-tert-butoxy-.alpha.-methylstyrene was
radically polymerized and fractionated, obtaining a
p-tert-butoxy-.alpha.-methylstyrene polymer having a Mw of 16,000
and a dispersity of 1.30. This is designated Polymer B.
A 500-ml flask was charged with 50 grams of Polymer A or B and 200
ml of acetone. The flask was then heated to 60.degree. C. An acid,
15% aqueous hydrochloric acid or trifluoroacetic acid, the amount
of which is shown in Table 1, was added dropwise to the flask over
about one hour and partial scission reaction was continued for 6
hours. The flask was cooled down. The resulting polymer was washed
with water, dried, and analyzed for a degree of splitting by
Fourier transform infrared spectroscopy (FT IR). The degree of
splitting was determined from the absorbance ratio of the
absorption peak at 1512 cm.sup.-1 attributable to phenyl group to
the absorption peak at 897 cm.sup.-1 attributable to t-butyl
group.
TABLE 1 ______________________________________ Degree of Acid
splitting No. Polymer Type Amount* (mol %) Resin
______________________________________ 1 A 15% HCl 0.5 mol 95 2 A
15% HCl 0.2 mol 80 C 3 A 15% HCl 0.1 mol 54 4 A CF.sub.3 COOH 1.0
mol 92 5 A CF.sub.3 COOH 0.5 mol 78 D 6 A CF.sub.3 COOH 0.25 mol 52
7 B 15% HCl 0.4 mol 82 8 B 15% HCl 0.2 mol 76 E 9 B 15% HCl 0.15
mol 64 ______________________________________ *The amount (mol) of
acid is per mol of OR.sup.2 (butoxy) group in the polymer.
Example 1
A resist solution was prepared by dissolving 9.6 grams of Resin C
(poly-tert-butoxystyrene/polyhydroxystyrene) obtained in Synthesis
1, 0.48 grams of a compound of the formula (6) shown below as an
acid release agent, and 1.92 grams of
2,2-bis[p-(t-butoxycarbonyloxy)phenyl]propane as a dissolution
inhibitor in 66 grams of diethylene glycol dimethyl ether and
passing the mixture through a 0.2-.mu.m mesh filter. ##STR12##
The resist solution was spin coated on a silicon substrate at 2,000
rpm and pre-baked on a hot plate at 100.degree. C. for 2 minutes.
The resist film was 0.8 .mu.m thick. The resist film was exposed to
a pattern using an electron beam at an accelerating voltage of 30
kV, post-exposure baked (PEB) at 85.degree. C. for 90 seconds,
developed for one minute with an aqueous solution of 2.4%
tetramethylammonium hydroxide (TMAH), and rinsed with water for 30
seconds. The resist had a D.sub.0 sensitivity of 7 .mu.C/cm.sup.2
and bore a positive pattern.
When deep-ultraviolet light or KrF excimer laser light (wavelength
248 nm) was used instead of the electron beam, the D.sub.0
sensitivity was 24 mJ/cm.sup.2.
A line and space pattern of 0.28 .mu.m could be resolved in the KrF
excimer laser exposure whereas a line and space pattern of 0.22
.mu.m could be resolved in the electron beam exposure.
Example 2
A resist film was prepared by the same procedure as in Example 1
except that Resin C was replaced by Resin D
(poly-tert-butoxystyrene/polyhydroxystyrene). The electron beam
sensitivity was 8.4 .mu.C/cm.sup.2 and the KrF sensitivity was 28
mJ/cm.sup.2, indicating equivalent resolution to Example 1. It was
also found that the pattern resulting from KrF laser exposure had
perpendicular side walls.
Example 3
A resist film was prepared by the same procedure as in Example 1
except that Resin C was replaced by Resin E
(poly-tert-butoxy-.alpha.-methylstyrene/polyhydroxystyrene) and an
onium salt of the formula (7) shown below was used as the acid
release agent. ##STR13##
It was found that PEB at 90.degree. C. for 90 seconds resulted in a
resist having a positive pattern. The electron beam sensitivity was
6.5 .mu.C/cm.sup.2. Under the developing conditions in Example 1,
this resist had good film retention as demonstrated by a film loss
of about 2% and a line and space pattern of 0.22 .mu.m could be
resolved. Evaluation was also made with exposure to KrF excimer
laser light to find full resolution of a line and space pattern of
0.28 .mu.m. Comparative Example 1
A solution of 20 grams of p-tert-butoxystyrene monomer and 0.40
grams of 2,2-azobisisobutylnitrile in 20 ml of toluene was subject
to reaction at 70.degree. C. for 5 hours in a nitrogen atmosphere.
The resulting polymer was washed with methanol and dried, obtaining
14 grams of poly-tert-butoxystyrene. On GPC analysis, the polymer
had a Mw of 9,000 and a dispersity of 1.90. The polymer was then
subject to partial scission reaction for 6 hours with 15% aqueous
hydrochloric acid in an amount of 3.0 mol per mol of butoxy group
in the polymer. The degree of splitting was 100%. The polymer was
washed and dried. It was then dissolved in 100 ml of pyridine. By
adding di-tert-butyl dicarbonate to the solution, the polymer was
tert-butoxycarbonylated. The t-Boc content was 20 mol% as measured
by NMR.
A resist solution was prepared using this polymer along with the
acid release agent, dissolution inhibitor and solvent used in
Example 1. As in Example 1, exposure was made to KrF excimer laser
light by means of a stepper. As a result, a pattern could be
resolved up to 0.4 .mu.m, but no finer pattern could be
resolved.
Synthesis 2
A 500 -ml flask was charged with 2.4 grams of
2,2'-azobisisobutylnitrile, 47.8 grams of p-tert-butoxystyrene,
11.2 grams of p-methoxymethoxystyrene, and 120 ml of benzene and
purged with nitrogen. The mixture was subject to polymerization at
90.degree. C. for 6 hours. The resulting polymer was washed with
methanol and dried. On GPC analysis, the polymer had a Mw of 16,500
and a dispersity of 1.87. The yield was 72% .
The polymer was further dissolved in a benzene/methanol solvent
mixture for fractionation. The polymer was dried again, obtaining
Polymer F of the rational formula shown below having a Mw of 14,500
and a dispersity of 1.30. On proton-NMR analysis of the polymer,
there appeared peaks at 1.5 ppm attributable to tert-butyl group,
at 4.8 ppm attributable to --O--CH.sub.2 --O, and at 3.1 ppm
attributable to --O--CH.sub.3. In formula (F), c':d=0.8:0.2.
##STR14## Synthesis 3
As in Synthesis 2, p-tert-butoxy-.alpha.-methylstyrene and
p-methoxymethoxystyrene were radically polymerized and
fractionated, obtaining Polymer G of the rational formula shown
below. It had a Mw of 17,500 and a dispersity of 1.25. In formula
(G), c':d =0.9:0.1. ##STR15##
Synthesis 4
To remove water and other impurities from p-tert-butoxystyrene and
p-methoxymethoxy-.alpha.-methylstyrene monomers, these monomers
were distilled in the presence of a purifying aid such as CaH.sub.2
and sodium benzophenone. A 1-liter flask was charged with 550 ml of
tetrahydrofuran (THF) as a solvent and 3.3.times.10.sup.-4 mol of
n-butyllithium as a polymerization initiator and cooled to
-78.degree. C. To the flask was added a mixture of the purified
monomers. Upon polymerization for one hour, the reaction solution
turned red. Methanol was added to the reaction solution to stop
polymerization. The reaction solution was poured into methanol
whereby the polymer was precipitated. The polymer was separated and
dried, obtaining 48 grams of a white polymer H of the rational
formula shown below. On GPC analysis, it was found to be a narrow
disperse polymer having a Mw of 15,000 and a dispersity of 1.03. On
proton-NMR analysis, there appeared peaks at 1.5 ppm attributable
to tert-butyl group, at 4.8 ppm attributable to--O--CH.sub.2 --O--,
and at 3.1 ppm attributable to --O--CH.sub.3. In formula (H),
c':d=0.7:0.3. ##STR16##
Synthesis 5
As in Synthesis 4, an equimolar mixture of p-tert-butoxystyrene and
tetrahydropyranyloxystyrene was subject to living polymerization in
THF solvent at -70.degree. C. The reaction solution was washed with
methanol, precipitated, and dried, obtaining 50 grams of a white
polymer I of the rational formula shown below. On GPC analysis, it
was found to be a narrow disperse polymer having a Mw of 13,500 and
a dispersity of 1.05. In formula (I), c':d=0.8:0.2. ##STR17##
Synthesis 6
As in Synthesis 2 , an equimolar mixture of p tert-butoxystyrene
and trimethylsiloxystyrene was radically polymerized, obtaining
Polymer J of the rational formula shown below. It had a Mw of
14,200 and a dispersity of 1.06 . In formula (J) , c':d=0.8:9.2 .
##STR18##
A 500-ml flask was charged with 40 grams of each of Polymers F to J
in Synthesis Examples 2 to 6. The polymer was dissolved in 200 ml
of acetone. By adding an acid, the type and amount of which are
shown in Table 2, to the flask, partial scission reaction was
carried out. The flask was cooled down. The resulting polymer was
washed with water, dried, and analyzed by proton-NMR to determine
the residual amounts of a tert-butyl group and a R.sup.6 group
(methoxymethyl, tetrahydropyranyl or trimethylsilyl group). The
results are shown in Table 2.
TABLE 2 ______________________________________ Final polymer
Starting Acid R.sup.6 No. polymer Type Amount* t-butyl (mol) Resin
______________________________________ 11 F dry HCl 0.4 mol 0.05
0.2 K 12 F dry HCl 0.2 mol 0.20 0.2 13 G dry HCl 0.2 mol 0.25 0.1
14 G CF.sub.3 COOH 0.4 mol 0.07 0.1 L 15 G CF.sub.3 COOH 0.25 mol
0.15 0.1 16 H dry HCl 0.3 mol 0.10 0.3 M 17 H dry HCl 0.15 mol 0.25
0.3 18 I dry HCl 0.40 mol 0.05 0.2 N 19 I dry HCl 0.30 mol 0.10 0.2
20 J dry HCl 0.40 mol 0.05 0.2 O 21 J dry HCl 0.30 mol 0.08 0.2
______________________________________ *The amount (mol) of acid is
per mol of OR.sup.4 (butoxy) group in the polymer.
The resulting resins K to O are represented by the following
rational formulae. ##STR19##
It is understand that by reacting p-tert-butoxystyrene or
p-tert-butoxy-.alpha.-methylstyrene with
p-isopropoxymethoxystyrene, p-tetrahydrofuranyloxystyrene or
p-tert-butoxy-carbonyloxystyrene in a similar manner, there are
obtained polymers of rational formula (2) wherein R.sup.6 is an
isopropoxymethyl, tetrahydrofuranyl or tert-butoxycarbonyl
group.
Example 4
A resist solution was prepared by dissolving 9.6 grams of Resin K
(poly-p-tert-butoxystyrene/poly-p-methoxymethoxy-styrene/polyhydroxystyren
e copolymer) obtained in Synthesis 2, 0.48 grams of a compound of
formula (6) shown below as an acid release agent, and 1.92 grams of
2,2-bis[p-(t-butoxycarbonyloxy)phenyl]propane as a dissolution
inhibitor in 66 grams of diglyme and passing the mixture through a
0.2 .mu.m mesh filter. ##STR20##
The resist solution was spin coated on a silicon substrate at 2,000
rpm and pre-baked on a hot plate at 100.degree. C. for 2 minutes.
The resist film was 0.9 .mu.m thick. The resist film was exposed to
a pattern using an electron beam at an accelerating voltage of 30
kV, post-exposure baked (PEB) at 85.degree. C. for 90 seconds,
developed for one minute with an aqueous solution of 2.4%
tetramethylammonium hydroxide (TMAH), and rinsed with water for 30
seconds. The resist had a D.sub.0 sensitivity (or electron
sensitivity) of 5 .mu.C/cm.sup.2 and bore a positive pattern.
When deep-ultraviolet light or KrF excimer laser light (wavelength
248 nm) was used instead of the electron beam, the D.sub.0
sensitivity was 15 mJ/cm.sup.2.
A line and space pattern of 0.26 .mu.m could be resolved in the KrF
excimer laser exposure whereas a line and space pattern of 0.25
.mu.m could be resolved in the electron beam exposure.
Example 5
A resist film was prepared by the same procedure as in Example 4
except that Resin L was used. The electron beam sensitivity was 7.4
.mu.C/cm.sup.2 and the KrF sensitivity was 26 mJ/cm.sup.`,
indicating equivalent resolution to Example 4. It was also found
that the pattern resulting from KrF laser exposure had
perpendicular side walls.
Example 6
A resist film was prepared by the same procedure as in Example 4
except that Polymer M and an onium salt of formula (7) shown below
as the acid release agent were used. ##STR21##
It was found the PEB at 90.degree. C. for 90 seconds resulted in a
resist having a positive pattern. The electron beam sensitivity was
6.5 .mu.C/cm.sup.2. Under the developing conditions in Example 4,
this resist had good film retention as demonstrated by a film loss
of about 2% and line and space pattern of 0.22 .mu.m could be
resolved. Evaluation was also made with exposure to KrF excimer
laser light to find full resolution of a line and space pattern of
0.27 .mu.m.
Example 7
A resist solution was prepared by the same procedure as in Example
6 except that Polymer N was used, and coated on a wafer. The resist
film was exposed in a dose of 40 mJ/cm.sup.2 by means of an excimer
stepper, baked (PEB) at 90.degree. C. for 90 seconds, and developed
with 2.38% TMAH. A line and space pattern of 0.26 .mu.m having
perpendicular side walls could be resolved.
Example 8
A resist film was similarly prepared except that Polymer O and
t-butylidodonium trifulate as an acid release agent were used, and
similarly evaluated. A fine pattern was formed as in Example 7.
Example 9
Equivalent resolution was achieved when polymers of formula (2)
wherein R.sup.6 is an isopropoxymethyl, tetrahydrofuranyl or
tert-butoxycarbonyl group are used.
Comparative Example 2
A solution of 20 grams of p-tert-butoxystyrene monomer and 0.40
grams of 2,2-azobisisobutylnitrile in 20 ml of toluene was subject
to reaction at 70.degree. C. for 5 hours in a nitrogen atmosphere.
The resulting polymer was washed with methanol and dried, obtaining
14 grams of poly-tert-butoxystyrene. On GPC analysis, the polymer
had a Mw of 9,000 and a dispersity of 1.90. The polymer was then
subject to partial scission reaction for 6 hours with 15% aqueous
hydrochloric acid in an amount of 3.0 mol per mol of butoxy group
in the polymer. The degree of splitting was 100%. The polymer was
washed and dried. It was then dissolved in 100 ml of pyridine. By
adding di-tert-butyl dicarbonate to the solution, the polymer was
tert-butoxycarbonylated. The t-Boc content was 20 mol% as measured
by NMR.
A resist solution was prepared using this polymer along with the
acid release agent, dissolution inhibitor and solvent used in
Example 4. As in Example 4, exposure was made to KrF excimer laser
light by means of a stepper. As a result, a pattern could be
resolved up to 0.4 .mu.m, but no finer pattern could be
resolved.
Synthesis 7
A 500-ml flask was charged with 2.4 Grams of
2,2'-azobisisobutylnitrile, 63.3 grams (0.36 mol) of
p-tert-butoxystyrene, 6.6 grams (0.04 mol) of p-methoxystyrene, and
120 ml of benzene and purged with nitrogen. The mixture was subject
to polymerization at 90.degree. C. for 6 hours. The resulting
polymer was washed with methanol and dried. On GPC analysis, the
polymer had a Mw of 16,500 and a dispersity of 1.67. The yield was
72%.
The polymer was further dissolved in a benzene/methanol solvent
mixture for fractionation. The polymer was dried again, obtaining
Polymer P of the rational formula shown below having a Mw of 14,500
and a dispersity of 1.30. On proton-NMR analysis of the polymer,
there appeared peaks at 1.5 ppm attributable to tert-butyl group
and at 3.1 ppm attributable to --O--CH.sub.3. In formula (P),
f':g=0.9:0.1. ##STR22##
Synthesis 8
As in Synthesis 7, p-tetrahydro-pyranyloxystyrene and
p-methoxystyrene were radically polymerized and fractionated,
obtaining Polymer Q of the rational formula shown below. It had a
Mw of 16,500 and a dispersity of 1.25. In formula (Q),
f':g=0.95:0.05. ##STR23##
Synthesis 9
To remove water and other impurities from
p-methoxymethoxy-.alpha.-methylstyrene and p-methoxystyrene
monomers, these monomers were distilled in the presence of a
purifying aid such as CaH.sub.2 and sodium benzophenone. A 1-liter
flask was charged with 550 ml of tetrahydrofuran (THF) as a solvent
and 3.3.times.10.sup.-4 mol of n-butyllithium as a polymerization
initiator and cooled to -78.degree.0 C. To the flask was added a
mixture of the purified monomers. Upon polymerization for one hour,
the reaction solution turned red. Methanol was added to the
reaction solution to stop polymerization. The reaction solution was
poured into methanol whereby the polymer was precipitated. The
polymer was separated and dried, obtaining 48 grams of a white
polymer R of the rational formula shown below. On GPC analysis, it
was found to be a narrow disperse polymer having a Mw of 15,000 and
a dispersity of 1.03. On proton-NMR analysis, there appeared peaks
at 4.8 ppm attributable to --O--CH.sub.2 --O-- and at 3.1 ppm
attributable to --O--CH.sub.3. In formula (R), f':g=0.95:0.05.
##STR24##
Synthesis 10
As in Synthesis 7, an equimolar mixture of p-trimethylsiloxystyrene
and p-methoxystyrene was radically polymerized in benzene solvent.
The reaction solution as washed with methanol, precipitated, and
dried, obtaining 50 grams of a white polymer S of the rational
formula shown below. On GPC analysis, the polymer was found to have
a Mw of 13,500 (calculated as poly-styrene) and a dispersity of
1.25. In formula (S), f':g=0.9:0.1. ##STR25##
A 500-ml flask was charged with 40 grams of each of Polymers P to S
in Synthesis Examples 7 to 10. The polymer was dissolved in 200 ml
of acetone. By adding an acid, the type and amount of which are
shown in Table 3, to the flask, partial scission reaction was
carried out. The flask was cooled down. The resulting polymer was
washed with water, dried, and analyzed by proton-NMR to determine
the residual amounts of a R.sup.8 group (methoxy group) and a
R.sup.7 group (tert-butyl, methoxymethyl, tetrahydropyranyl or
trimethylsilyl group). The results are shown in Table 3.
TABLE 3 ______________________________________ Start- ing Final
polymer poly- Acid methoxy R.sup.7 No. mer Type Amount* (mol %)
(mol) Resin ______________________________________ 31 P dry HCl 0.4
mol 0.10 0.15 T 32 P dry HCl 0.2 mol 0.10 0.20 33 Q conc. HCl 0.2
mol 0.05 0.16 34 Q CF.sub.3 COOH 0.4 mol 0.05 0.12 U 35 Q CF.sub.3
COOH 0.25 mol 0.05 0.10 36 R conc. HCl 0.3 mol 0.05 0.15 V 37 R
conc. HCl 0.15 mol 0.05 0.24 38 S conc. HCl 0.40 mol 0.10 0.10 W 39
S conc. HCl 0.30 mol 0.10 0.20
______________________________________ *The amount (mol) of acid is
per mol of OR.sup.7 group in the polymer.
The resulting resins T to W are represented by the following
rational formulae. ##STR26##
Example 10
A resist solution was prepared by dissolving 9.6 grams of Resin T
(poly-tert-butoxystyrene/poly-p-methoxystyrene/polyhydroxystyrene
copolymer) obtained in Synthesis 7, 0.48 grams of a compound of
formula (6) shown below as an acid release agent, and 1.92 grams of
2,2-bis[p-(t-butoxy-carbonyloxy)phenyl]propane as a dissolution
inhibitor in 66 grams of diglyme and passing the mixture through a
0.2 .mu.m mesh filter. ##STR27##
The resist solution was spin coated on a silicon substrate at 2,000
rpm and pre-baked on a hot plate at 100.degree. C. for 2 minutes.
The resist film was 0.95 .mu.m thick. The resist film was exposed
to a pattern using an electron beam at an accelerating voltage of
30 kV, post-exposure baked (PEB) at 85.degree. C. for 90 seconds,
developed for one minute with an aqueous solution of 2.4%
tetramethylammonium hydroxide (TMAH), and rinsed with water for 30
seconds. The resist had a D.sub.0 sensitivity of 5 .mu.C/cm.sup.2
and bore a positive pattern.
When deep-ultraviolet light or KrF excimer laser light (wavelength
248 nm) was used instead of the electron beam, the D.sub.0
sensitivity was 10 mJ/cm.sup.2.
A line and space pattern of 0.26 .mu.m was resolved in the KrF
excimer laser exposure whereas a line and space pattern of 0.25
.mu.m was resolved in the electron beam exposure.
Example 11
A resist film was prepared by the same procedure as in Example 10
except that Resin U was used. The electron beam sensitivity was 6.3
.mu.C/cm.sup.2 and the KrF sensitivity was 20 mJ/cm.sup.2,
indicating equivalent resolution to Example 10. It was also found
that the pattern resulting from KrF laser exposure had
perpendicular side walls.
Example 12
A resist film was prepared by the same procedure as in Example 10
except that Polymer V and an onium salt of formula (7) shown below
as the acid release agent were used. ##STR28##
It was found that PEB at 90.degree. C. for 90 seconds resulted in a
resist having a positive pattern. The electron beam sensitivity was
6.5 .mu.C/cm.sup.2. Under the developing conditions in Example 10,
this resist had good film retention as demonstrated by a film loss
of about 2% and a line and space pattern of 0.22 .mu.m was
resolved. Evaluation was also made with exposure to KrF excimer
laser light to find full resolution of a line and space pattern of
0.27 .mu.m.
Example 13
A resist solution was prepared by the same procedure as in Example
12 except that Polymer W was used, and coated on a wafer. The
resist film was exposed in a dose of 40 mJ/cm.sup.2 by means of an
excimer stepper, baked (PEB) at 90.degree. C. for 90 seconds, and
developed with 2.38% TMAH. A line and space pattern of 0.26 .mu.m
having perpendicular side walls could be resolved.
Example 14
A resist film was similarly prepared except that Polymer V and
t-butylidodonium trifulate as an acid release agent were used, and
similarly evaluated. A fine pattern was formed as in Example
13.
Comparative Example 3
A solution of 20 grams of p-tert-butoxystyrene monomer and 0.40
grams of 2,2-azobisisobutylnitrile in 20 ml of toluene was subject
to reaction at 70.degree. C. for 5 hours in a nitrogen atmosphere.
The resulting polymer was washed with methanol and dried, obtaining
14 grams of poly-tert-butoxystyrene. On GPC analysis, the polymer
had a Mw of 9,000 and a dispersity of 1.90. The polymer was then
subject to partial scission reaction for 6 hours with 15% aqueous
hydrochloric acid in an amount of 3.0 mol per mol of butoxy group
in the polymer. The degree of splitting was 100%. The polymer was
washed and dried. It was then dissolved in 100 ml of pyridine. By
adding di-tert-butyl dicarbonate to the solution, the polymer was
tert-butoxycarbonylated. The t-Boc content was 20 mol% as measured
by NMR.
A resist solution was prepared using this polymer along with the
acid release agent, dissolution inhibitor and solvent used in
Example 4. As in Example 4, exposure was made to KrF excimer laser
light by means of a stepper. As a result, a pattern could be
resolved up to 0.4 .mu.m, but no finer pattern could be
resolved.
Although some preferred embodiments have been described, many
modifications and variations may be made thereto in the light of
the above teachings. It is therefore to be understood that within
the scope of the appended claims, the invention may be practiced
otherwise than as specifically described.
* * * * *